Do o-rings shrink??

[tedm2]

I have twice purchased 5 packs of o-rings for a 290DPA for future use. Once from Sierra and once Volvo. Both times when I have needed them they were to small to stay in the grove on the lower unit. Is this normal that they not maintain size over a year?

 

[dennis461]

Even junk rubber would hold up for 5 years...
http://www.oringsusa.com/html/shelf_life.html

 

[RicardoMarine]

Generally they do not shrink while being stored.

If you are asking about the larger of the three lower unit O-rings, this one is generally a bit on the small side.
If installing it dry, they usually want to slip out of position.
Try giving it a gentle stretch right before installing it and try installing it with Perfect Seal or grease.

 

[Scarron]

The short answer is no, NBR [Nitrile] rubber does not shrink over time, it is however very susceptible to U.V. degradation [you'll spot the signs as it the surface will harden and develop loads of tiny cracks] so keep them stored in a black polythene bag and they'll last 10-15 years easily. As Rick suggests just lightly stretch them by hand before fitting

 

[RicardoMarine]

As Rick suggests just lightly stretch them by hand before fitting

Just to clarify here..... I suggested stretching this one only.
The rest of the AQ series O-rings fit near perfectly as they are.

 

[Iluvboating]

I'll my two cents to what has already been stated. When stored correctly and used correctly, O-rings should last a while.